This invention relates to an antitheft system for a motor vehicle which has a plurality of control units for controlling vehicle systems.
A system of this type is discussed, for example, in German Patent Document DE 30 45 345 A1. In such devices, however, the problem arises that by removing the control unit and reading the reference information (such as an image or code data stored therein), or by copying input testing information, it becomes possible for an unauthorized user to operate the control apparatus. This problem is aggravated by the fact that the control apparatus must be removed from time to time for legitimate reasons, such as in the case of a defect, and as a result, the reference information can be ascertained or changed.
It is an object of the present invention to provide an antitheft system of the initially mentioned type which prevents starting of the motor vehicle when testing information which is controlling with respect to a control apparatus is entered.
This and other objects and advantages are achieved by the antitheft system according to the invention, in which each of the several control units has stored therein a different reference code or information, and emits an acknowledgement code, which is transmitted to the other control units when an input test signal matches the stored reference information. Each control unit can be activated only when it has received an input test signal which matches the stored reference information, and in addition, it has also received the proper acknowledgement signals from each of the other control units.
Since different testing and reference information is used to activate at least two of the control units, the vehicle can be started only when the correct testing information for each of the control units is entered into the system. This input expediently takes place via a data bus. Thus, the discovery of the testing or reference information which controls one control unit is without any value, because it can be used to clear only the pertaining control unit.
Since the motor vehicle can be started only with a knowledge of all testing information, the starting of the motor vehicle by the unauthorized user requires the discovery of all testing information, which makes a theft of the motor vehicle virtually impossible.
In principle, it is possible to carry out a comparison of the input testing information with the reference information for each control unit in a centralized manner, for example, in an antitheft safety apparatus of a motor vehicle. However, the degree of protection that is afforded is clearly increased when the control units themselves carry out the comparison with the input testing information, which prevents manipulation at a central unit. Also, in this manner, the required overall expenditures are kept low.
It is particularly advantageous for the testing information to be put in during a joint input operation. The input may take place, for example, by means of a radio transmission path, for example, by infrared or radio signal or in a mechanical manner.
In a preferred embodiment, the testing and reference information comprise image information, which is distinguished by a relatively easy handling capacity, with a high information density. A particularly advantageous example for this purpose is the use of an authorized operator's finger print as image information. Such an access control system is disclosed for example in the journal VDI Nachrichten, No. 3, of Jan. 22, 1993, Page 13, in which the finger print has the function of a key. However, the use of this system within the scope of the present invention does not signify a simple application to motor vehicles, but differs in respect of the variety of the testing or reference information which is available for comparison in each of the control units. The finger print therefore does not have the quality of a single key, but rather, supplies a group of keys of which, in an extreme case, only one "fits" a control unit.
However, the use of the access control system known from the journal article is significant in that, there also, a series of images can be obtained from a finger print. Thus, in the antitheft system according to the invention, this means that one of the respective images is in each case controlling with respect to one of the control units. If these image data are acquired during a joint image taking operation, they may, within the scope of the invention; be used for taking the various testing information (=image information) in a joint input procedure.
In principle, it is possible to activate each of the control units when it receives the expected test information. However, as a result, it would then be possible to start the motor vehicle when only those control units are operating which are important for its operation, while less important control units may remain switched off. The degree of theft protection is thus increased when each of the control units emits an acknowledgement signal if the testing and the reference information correspond to one another, and each control unit can be activated only when acknowledgement signals are received from each of the other control units. It thus becomes impossible to manipulate and activate a single control unit, such as the drive assembly, because the start of the operation of the control units depends on the receipt of the acknowledgement signals from the other control units.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.